Prior art arrival-indicators function unreliably, often resulting in many erroneous triggerings, as well as many actual fault triggering situations which remain undetected. These problems are particularly accentuated in air-driven looms, so-called jet looms, which are extraordinarily rapid and which operate at such high speeds as 20 picks per second, in which event the arrival sensing must be executed under approximately 10-15.degree. of a whole machine cycle (5% of the cycle). This naturally places extremely high demands on the indicator proper and its associated electronics, in particular as regards sensitivity and speed. Moreover, prior art indicators with whose help a part of the above-outlined problems have been reduced or even wholly obviated have proved to be extremely uneven in connection with different weft yarns, which may reflect light to different extents. The problems have been accentuated in the employment of weft yarns with different colors and structures. In certain contexts, the problems have proved to be so intractable that no signals have been emitted at all on the use of certain weft threads or weft yarns.